The present invention relates generally to medical catheters, and more specifically to a magnetic device and method for facilitating the exchange of catheters during a medical procedure.
Medical catheters of different types are used for a variety of purposes, including coronary angioplasty and angiography. Medical catheters generally have a proximal hub, a body, and a distal tip portion. The body is formed of a flexible, relatively narrow tubular material having sufficient length to traverse a path from an external incision to an internal region of interest within the body of the patient. The proximal hub enables the catheter to be coupled with medical equipment which is used to perform a medical procedure at the distal tip portion.
Many medical catheters are designed for use in conjunction with a guidewire having a distal tip which guides the distal end of the catheter. The guidewire is usually formed of a stainless steel and platinum alloy, and its distal tip is often bent for "steering" the guidewire tip among the body passageways of the patient by twisting the proximal end of the guidewire as it is advanced and retracted. Guidewires are relatively long, usually over 175 centimeters, and preferably approximately 200 centimeters in length. Guidewires are also relatively thin, approximately 0.009 to 0.038 inches in diameter, preferably having a diameter of approximately 0.014 inches. In addition, the distal tip of the core wire is generally much thinner than the balance of the guidewire, on the order of 0.004 inches in diameter.
In a typical medical procedure such as angiography or angioplasty, the catheter is usually preloaded onto the guidewire by feeding the guidewire through the catheter until a relatively short distal portion of guidewire, approximately 1.25 to as long as 10.0 inches, extends distally beyond the tip of the catheter, with a portion of the guidewire extending proximally from the catheter hub. The preloaded catheter and guidewire are then inserted into the body of the patient, steering them into the proper passageways, until the tip of the guidewire is disposed in the desired region. In the alternative, the guidewire may be first inserted within the patient using the "bare wire" technique, and the tubular catheter subsequently inserted by sliding it over the guidewire.
In the particular case of balloon angioplasty, a guiding catheter is initially placed through the femoral artery into the aorta, and its tip is disposed near to the coronary arteries which branch from the aorta, in a region called the ostium. The guiding catheter thus acts as a conduit to access the various coronary arteries with a guidewire and subsequently a balloon catheter. The guiding catheter is constructed of plastic tubing approximately one meter in length, and having a inside diameter substantially within the range of 5 to 9 French size. "French size" is defined as an object having a major diameter of a multiple of 0.013 inches.
Balloon angioplasty catheters and other associated apparatus are described in U.S. Pat. No. 4,906,244, issued on Mar. 6, 1990 to Pinchuk et al., the disclosure of which is incorporated herein by reference. The balloon catheter is an elongated flexible plastic member defining at least two longitudinal passages, or lumens, and preferably having a substantially inelastic balloon located near its distal tip. One lumen accepts the guidewire, while the other lumen allows communication of inflation fluid with the interior of the balloon to inflate it at pressures which usually range from four to twelve atmospheres, to conduct the angioplasty.
The guidewire and balloon catheter assembly is inserted through the guiding catheter until the balloon is near the distal end of the guiding catheter. The balloon catheter is then halted, while the guidewire is advanced from the distal end of the guiding catheter until the distal tip of the guidewire traverses a restricted region of the artery. The guidewire is then held stationary while the balloon catheter is advanced, following the path of the guidewire which is already in place. When the balloon is located in the restricted region, inflation fluid is injected through the inflation lumen, causing the balloon to inflate and reopen the artery to allow sufficient blood flow.
Medical procedures often require the use of different catheters in the same internal region of the body. It often becomes necessary to exchange one catheter for another, and to reposition a distal tip portion of the second catheter in the same location as the first. It is highly desirable to leave the guidewire in place for the duration of the medical procedure, including during the exchange of catheters. If the guidewire is ever removed from the desired position, it must again be steered back to its original position. However, this subsequent navigation may become exceedingly difficult because of the three dimensional complexity of the body passageways. Another reason for maintaining the guidewire in place is that, whenever a foreign object such as the guidewire or a catheter is introduced within a blood vessel, the vessel may spasm and generally constrict along a substantial portion of its length. If the guidewire is removed while the artery is contracted, it may become practically impossible to re-insert the guidewire through the constricted artery.
The problem is that the action of either withdrawing or inserting a catheter over a guidewire imparts a longitudinal force due to friction which tends to dislodge the guidewire. This frictional force between the guidewire and the catheter guidewire lumen is relatively strong, because the difference between the guidewire diameter and the inner diameter of the catheter can be as small as 0.002 inches. Even when the guidewire is provided with a lubricious coating, the guidewire must be restrained from moving relative to the patient. As a result, if the catheter were withdrawn over the proximal end of the guidewire without restraining it, the guidewire would be withdrawn with the removal of the catheter. Accordingly, if a catheter is inserted over a bare wire, the guidewire will tend to be pushed further into the anatomy of the patient.
The reason it is difficult to hold the guidewire stationary is that the majority of the guidewire is inaccessible inside the patient. After the guidewire is in place, the proximal end of the guidewire extends approximately ten inches externally from the body of the patient. At some point during the insertion or withdrawal of a catheter from the guidewire, the entire external portion of the guidewire will be surrounded by the catheter. As a result, neither the internal portion of the guidewire within the body nor the external guidewire portion within the catheter can be conveniently held, to restrain frictional movement of the guidewire with the catheter.
Moreover, the first catheter must be withdrawn entirely from the guidewire before a subsequent catheter may be inserted over the guidewire. Because the full length of the tubular catheter is much longer than the proximal external portion of the guidewire, there is no convenient way to physically anchor the guidewire. As a result, exchanging a first catheter for a second catheter is currently difficult and cumbersome because the relatively inaccessible guidewire must be held stationary.
Previous methods have included the use of an "exchange length" guidewire which is essentially twice the desired length. Such an exchange length guidewire has sufficient length to traverse a path from the point of entry into the patient to a blood vessel stenosis, while providing an external portion which is longer than the full length of the catheter. Such extremely long guidewires are obviously inconvenient and undesirable.
Another method of exchanging catheters provides a removable guidewire extension which is attached to the proximal end of the guidewire, allowing the guidewire to be held in place as the full length of a catheter is removed or inserted, temporarily doubling the length of the guidewire during the exchange. The guidewire length is thus extended such that the proximal end of the guidewire extension can remain proximal from the proximal end of the catheter, even when the catheter is fully threaded onto the guidewire yet entirely external to the patient. An additional assistant is required to manually hold the proximal portion of these extremely long guidewires stationary, preventing guidewire movement during the withdrawal or insertion of the catheter.
The pioneer patent regarding catheter exchange is entitled "Magnetic Guidewire Coupling for Vascular Dilatation Apparatus", U.S. Pat. No. 5,269,759, filed on Jul. 28, 1992, which was issued to Hernandez et al. on Dec. 14, 1993. This patent teaches the concept of utilizing magnetic force to inhibit longitudinal movement of the guidewire relative to the guiding catheter and to the patient, even while a catheter is being withdrawn or inserted over the guidewire. Hernandez discloses a first magnetic clement affixed to the guidewire and a second magnetic clement which is proximate to but external from the guiding catheter to apply a magnetic force to inhibit longitudinal sliding motion of the guidewire within the guiding catheter. The guidewire is therefore magnetically, rather than physically, anchored in a stationary position relative to the patient. Hernandez teaches providing an annular magnet to create a magnetic field in the vicinity of the proximal end of the catheter for magnetically attracting a magnetic portion of the guidewire.
The parent of the present patent application is entitled "Magnetic Exchange Device for Catheter" by Viera, Ser. No. 08/189,453, and was filed on Jan. 31, 1994. Viera teaches a ferromagnetic rod having numerous integral rings, which ;may be affixed to the guidewire and a magnetic retainer having a stack of permanent ring magnets separated by ferromagnetic rings. Viera is able to provide a stronger magnetic field by providing a plurality of magnets.
It is accordingly desirable to provide a magnetic device for facilitating the exchange of medical catheters which provides a strong magnetic resistance against longitudinal slipping of the guidewire in a relatively simple device which occupies a relatively small volume. It is further desirable to provide a magnetic device defining a magnetic channel for removably accepting a portion of a guidewire surrounded by a catheter, which furthers incorporates a mechanical retainer for releasably securing the catheter and guidewire within the magnetic channel, while allowing longitudinal withdrawal and insertion of a catheter.
The unique magnetic device of the present invention provides a magnetic retainer defining a magnetic channel for removably accepting a portion of a guidewire, in which the device imposes a magnetic force on the guidewire which tends to inhibit longitudinal motion of the guidewire with respect to the magnetic device of the present invention.
These and various other objects, advantages and features of the invention will become apparent from the following description and claims, when considered in conjunction with the appended drawings.